37kW in, 30 kW out to radiators (and 7kW up the chimney) if I’ve read that correctly.
Reassurance before accepting a quote for a new boiler
- Thread starter wannadie
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37kW in, 30 kW out to radiators (and 7kW up the chimney) if I’ve read that correctly.
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You might want to consider a heat only boiler, rather than a system boiler. Means the pump and valves are external to the boiler, allowing you / your installer to choose them, and making you less dependent on manufacturer's prices. Can still be a sealed system with modern boilers.
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I think the benefit of having those components covered under a 7 or 10 year warranty within the system boiler and saving a bit of space is worth going system for us.
Speaking as a non-professional, non-qualified, slightly-above-average* DIYer (i.e. take the following with a pinch of salt!) I'd give you one piece of advice I wish I'd understood more before having our system replaced...
Do a bit of proper research on how to calculate the correct sizing of radiators - check one of my previous threads https://www.diynot.com/diy/threads/oversizing-radiators-how-much.530890/ for info. My experience is that not all boiler installers are the same as proper heating engineers, and are great at swapping boilers and components, but not always so great at the overall system design. If you like and trust the installer you've got but aren't convinced on this side of things, do your own research and work with them to design the system together?
* based on my own ratings, of course.
Do a bit of proper research on how to calculate the correct sizing of radiators - check one of my previous threads https://www.diynot.com/diy/threads/oversizing-radiators-how-much.530890/ for info. My experience is that not all boiler installers are the same as proper heating engineers, and are great at swapping boilers and components, but not always so great at the overall system design. If you like and trust the installer you've got but aren't convinced on this side of things, do your own research and work with them to design the system together?
* based on my own ratings, of course.
Heat output.
You don't say whether your 3-port valve is either/or (Honeywell W-plan) or mid-position (Y-plan). If it's W-plan the cylinder stat must be satisfied before CH is available. But that's not usually a problem. Cylinder heat loss is small if it's well insulated (preferably pre-insulated with foam) the heat lost goes into the house anyway. If it's Y-plan you can have HW or CH or both.
3 port valve is Y Plan. Programmable timer is very vintage so maybe this is the problem? Going to be replaced with a Nest.
Thank you everyone who has responded. I am learning so much. Forums are great.
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A job for tonight!
It's an even higher output boiler than we thought! Do you know what setting it's currently on? I assume it doesn't have 3 switchable settings, but varied continuously by adjusting the burner pressure at the gas valve, but you or somebody else might tell me I'm wrong. If you don't know the setting it can be checked by measuring the gas pressure with a manometer. But if it's a very old boiler it could be scaled up, with efficiency below nameplate data.
Once you know the setting, and knowing whether the current boiler seems borderline, about right, or OTT, should give you an idea about what you need from the new one, in addition to a calculated figure based on property details. Sounds like a biggish place, lots of rads, but I'd be surprised if 30kW output wasn't plenty.
If the timer works OK I doubt it is causing poor economy.
The table you show is for a Glow-worm Ultimate 120FF.
So far as heating the house is concerned, the important number is the heat output as this is what goes into the water flowing through the rads. Heat input is what you pay for; the difference is due to the efficiency (or lack of it) of the boiler.
The table shows three figures, min, medium and max. These allow the installer to set the boiler to the appropriate output for the house. The chosen setting should be indicated on the data plate inside the boiler. If no indicator, assume the maximum, i.e 35.17kW.
One of my previous houses was a 5-bed Edwardian semi, over three floors, with solid walls and mostly single glazed windows. The heating and hot water was provided by a 24kW boiler.
If you want to have a go at calculating your actual heat loss, try the Myson Heat Loss Manager.
Without seeing the house it’s hard to judge , Vaillant system 37 kw can be range rated , would have thought you would need 28 mm for gas especially if you have other gas appliances
The ultimate 120ff is 78.1
% effecient so flat out on 5 it generates 27kw of usable heat before losses.
A 36/37 kW will need minimum 28mm meter Union, Swept bends and 28mm pipe will be borderline will still pull the inlet down to about 18.5mb at max output.
A 630 system boiler would easily heat the system. Make sure you get a ecotec Pro (stainless hex) and not the (pura/energy clone Alu hex).
The 3 port needs binning, go with 2 two ports and a proper bypass.
% effecient so flat out on 5 it generates 27kw of usable heat before losses.
A 36/37 kW will need minimum 28mm meter Union, Swept bends and 28mm pipe will be borderline will still pull the inlet down to about 18.5mb at max output.
A 630 system boiler would easily heat the system. Make sure you get a ecotec Pro (stainless hex) and not the (pura/energy clone Alu hex).
The 3 port needs binning, go with 2 two ports and a proper bypass.
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